Can I write 8051 programs in "Borland's Turbo Assemmbler"

No.

Borland's Turbo Assemmbler is a Native assembler for x86 processors in a PC environment; you need a Cross Assembler to produce code for the 8051 processor.
See this earlier item, where I explained the difference between a Native- and a Cross-Compiler:
http://www.8052.com/forum/read.phtml?id=15760
The same distinction applies to Native- and a Cross-Assemblers.

There are many PC-hosted Cross-Assemblers available for the 8051 - Metalink is just one.
Confusingly, I think there is a cross-assembler called TASM - but it has no relation to Borland's Turbo Assembler!